None of the vibration monitoring and recording devices previously used in environmental work area studies has been directed toward monitoring the natural frequencies of the human spine. While numerous methods and apparatus for the frequency-monitoring of vibrational environments have been employed in the prior art, these previously employed systems generally measure vibrations of the environment where the events under analysis are oscillatory or periodic, and are of a substantially non-transient nature. There is a definite need for means to monitor and log transient events as short as a half cycle in duration. This need is not met by the use of the analog filtering techniques employed in the prior art vibration monitoring systems. There is also a definite need for accurately measuring and recording certain low frequency vibrations of particular importance with regard to their effects on the human spinal system, particularly in a seated position of the human body. Thus, rather than measuring the response of a system to a known repetitive input impulse, the characteristics of the driving input impulses should be measured and recorded, and quantitative indications of a given vibratory environment should be obtained with respect to those frequencies affecting the human spine. The prior art systems do not monitor the important specific frequency ranges of vibratory stress and do not impose suitable amplitude of acceleration thresholds before counting the events.
A preliminary search of the prior U.S. patents revealed the following U.S. patents of interest:
______________________________________ Brown et al, 3,393,557 Sohoel 3,554,012 Warner, 3,580,056 Lynas et al, 3,641,550 Shimauchi et al, 4,041,783 Weberhofer, 4,078,434 Avery, 4,167,877 ______________________________________